The disclosure of Japanese Patent Application No. 2000-090178 filed on Mar. 29, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates generally to an upper support used in a vehicle suspension system for supporting a piston rod of a shock absorber to a body of the vehicle, in a vibration-damping manner, and more particularly, to an upper support which is usable in a so-called xe2x80x9cinput separation typexe2x80x9d suspension system, wherein the upper support elastically support the piston rod of the shock absorber to the body of the vehicle, independently of a suspension spring of the suspension system.
2. Description of the Related Art
A wheel suspension assembly for an automotive vehicle includes a suspension spring and a shock absorber. The suspension assembly is interposed between a suspension arm or other members connected to a wheel of the vehicle and a body of the vehicle, for pivotally supporting the suspension arm to the vehicle body in a vibration-damping manner. In general, the shock absorber is secured at one end of its piston rod to a part of the vehicle body via a suspension upper support, for reducing or attenuating vibrations transmitted through the shock absorber into the vehicle body.
A known example of the above type of upper support is disclosed in Japanese Patent Laid-Open Publication No. JP-A-11-94007. The disclosed upper support includes: an inner member made of metal; an outer sleeve made of metal and disposed outwardly of the inner member in a radial direction perpendicular to an axial direction of the inner member with a predetermined spacing therebetween; and an rubber elastic body interposed between the inner member and the outer sleeve for elastically connecting therebetween. The outer sleeve has an upper and a lower stopper portions formed at its axially opposite open end portions, respectively, so as to protrude radially inward direction. The disclosed upper support further includes an upper and a lower elastic protrusions which protrude axially outwardly from the inner member in opposite axial directions so that the upper and lower elastic protrusions are held in abutting contact with the upper and lower stopper portions of the outer sleeve, respectively. The upper support constructed as described above is fixed at its inner member to the piston rod of the shock absorber, and is fixed at its outer sleeve to the vehicle body, for thereby elastically supporting the piston rod of the shock absorber with respect to the vehicle body.
However, the disclosed upper support with such conventional structure has a problem that it is likely to generate unusual sound or noise due to sliding or abutting contacts of the rubber elastic body with the outer sleeve member, upon application of high vibrational loads to the upper support in the axial, radial, inclined, torsional and other directions.
As a method to cope with the problem, it has been proposed in the above-indicated publication a modified structure of the upper support in which the rubber elastic body is bonded at its outer surface to the outer sleeve. However, this upper support with the modified structure requires a specific manufacturing step, e.g., an application of the adhesives to the outer sleeve, upon manufacturing thereof, thereby lowering the production efficiency of the upper support, and thereby increasing the cost of manufacture of the upper support. Further, the upper support with the modified structure may possible suffer from deterioration in its noise control effect, due to possible variations in bonding strength between the rubber elastic body and the outer sleeve. The variations of the bonding strength may cause partial debonding or separation of the rubber elastic body from the outer sleeve, upon application of an excessively large load to the upper support, or due to the aging of the upper support.
It is therefore an object of the present invention to provide an upper support for a vehicle suspension system, which is preferably applicable to an input-separation type suspension system, and which has a novel and simple structure for eliminating or reducing noises generated upon application of a load thereto.
The above and other objects of this invention may be attained according to the following modes of the invention. Each of these modes of the invention is numbered like the appended claims and depends from the other mode or modes, where appropriate, to indicate possible combinations of elements or technical features of the invention. It is to be understood that the principle of the invention is not limited to those modes of the invention and combinations of the technical features, but may otherwise be recognized based on the thought of the present invention that disclosed in the whole specification and drawings or that may be recognized by those skilled in the art in the light of the disclosure in the whole specification and drawings.
(1) An upper support for a suspension system, which is interposed between a body of a vehicle and a shock absorber of the vehicle for elastically supporting the shock absorber with respect to the body independently of a suspension spring of the suspension system, the upper support including: (a) an inner member connectable to a piston rod of the shock absorber; (b) an outer sleeve member which is disposed outwardly of the inner member in a radial direction perpendicular to an axial direction of the inner member with a spacing therebetween, and which is connectable to the body of the vehicle, the outer sleeve member having a first and a second stop portion formed at respective axially opposite open end portions thereof so as to protrude radially inwardly; (c) an elastic body interposed between an outer circumferential surface of the inner member and an inner circumferential surface of the outer sleeve member which is opposed to the outer circumferential surface of the inner member in the radial direction, the elastic body being secured at an inner circumferential surface thereof to the outer circumferential surface of the inner member, while being closely contact at an outer circumferential surface thereof with the inner circumferential surface of the outer sleeve member, the elastic body being held in abutting contact at axially opposite end faces thereof with the first and second stop portions of the outer sleeve member, respectively; and (d) a first and a second elastic protrusion protruding outwardly from the inner member in opposite axial directions, the first and second elastic protrusions being brought into abutting contact with the first and second stop portions of the outer sleeve member, respectively. The elastic body is compressed by the outer sleeve member in the radial direction so that the elastic body exhibits a shear strain of not greater than 1, upon application of an axial load of 1000N between the inner member and the outer sleeve member in a primary load receiving direction.
In the upper support constructed according to the present invention, the elastic body is subjected to a preload in the radial direction, namely the elastic body is previously compressed in the radial direction by a radial compression force having a value not smaller than a predetermined level. This arrangement makes it possible to decrease or minimize an amount of strain or deformation of the elastic body upon application of loads to the upper support. This arrangement also permits an increase of a frictional resistance at an interface formed between the outer circumferential surface of the elastic body and the inner circumferential surface of the outer sleeve, thereby preventing or minimizing a relative displacement between the elastic body and the outer sleeve at the interface. Therefore, the upper support of this invention is capable of minimizing uncomfortable sounds or noises caused by the relative displacement of the elastic body and the outer sleeve at the interface, upon application of the loads to the upper support.
In particular, the elastic body is subjected to the radial compression force under the specific condition, namely, with the axially opposite end faces of the elastic body held in abutting contact with the first and second stopper of the outer sleeve, respectively, for thereby limiting a free displacement of the elastic body in the opposite axially outward directions. This ensures a stable application of the radial preload to the elastic body with efficiency, whereby the upper support can exhibit a desired noise preventing effect with high stability.
It is noted that the shear strain xe2x80x9cxcex5xe2x80x9d of the elastic body is represented by the following formula (1):
xcex5=({square root over ( )}(B2+xcex42))/bxe2x80x83xe2x80x83(1)
where,
b=radial length of elastic body which is measured with no radial load applied to the elastic body (i.e., radial distance between outer circumferential surface of the inner member and the outer circumferential surface of the elastic body)
B=radial length of elastic body which is measured with radial load applied to the elastic body
xcex4=actual amount of axial displacement of the inner member relative to the outer sleeve upon application of 1000N load to the upper support in a bound direction as a primary load receiving direction.
According to one advantageous arrangement of this mode (1), the elastic body may be arranged to exhibit the shear strain of not grater than 1, upon application of a 1000N load in a rebound direction, thereby eliminating or minimizing the noises upon application of the rebound load to the upper support.
In this mode (1), the configurations and structures of the inner member and the outer sleeve are not particularly limited. According to another advantageous arrangement of this mode (1), the outer circumferential surface of the inner member and the inner circumferential surface of the outer member comprise respective cylindrical surfaces which are opposed to each other in the radial direction, and which are elastically connected with each other by the elastic body interposed therebetween. According to yet another advantageous arrangement of this mode (1), the inner member includes an annular connecting portion extending in the radial direction perpendicular to the axial direction thereof, the annular connecting portion being opposed at an outer circumferential surface thereof to the inner circumferential surface of the outer sleeve in the radial direction, while being opposed at axially opposite first and second end faces thereof to the first and second stop portions thereof, respectively, in the axial direction of the inner member, the first elastic protrusion being disposed between the first stop portion and the first end face of the annular connecting portion, while the second elastic protrusion being disposed between the second stop portion and the second end face of the annular connecting portion. In still another advantageous arrangement of this mode (1), the outer sleeve member is constituted by an hollow cylindrical metallic member having the first stop portion integrally formed at one of axially opposite open end portions so as to extend radially inwardly, the inner member and the elastic body fixed to the outer circumferential surface of the inner member is inserted from the other open end portion of the outer sleeve member and fitted into the outer sleeve member, and then an annular disk shaped metallic member is superposed on and fixed to the other open end portion of the outer sleeve to thereby form the second stop portion. Preferably, the annular disk shaped metallic member and the other open-end portion of the outer sleeve member may have respective fixing plates in the form of outward flanges as integral parts. These fixing plates of the metallic member and the outer sleeve member are superposed on each other and serve as a fixing portion of the outer sleeve member at which the outer sleeve member firmly fixed to the vehicle body.
Alternatively, in a still further advantageous arrangement of this mode (1), the outer sleeve is a split structure consisting of a pair of cylindrical metallic members each having the first or second stop portion integrally formed at one of axially opposite open end portions thereof so as to extend in a radially inward direction, the pair of cylindrical metallic members are press-fitted onto respective axially opposite end portions of the elastic body, and are butted together at the other axially opposite open end portions thereof in the axial direction. Preferably, each of the pair of the cylindrical metallic members has a fixing plate in the form of outward flange, which is integrally formed at the other axially opposite open-end portion thereof, which is remote from the corresponding stop portions. The fixing plates of the pair of cylindrical metallic members are superposed on each other in the axial direction and serve as a fixing portion of the outer sleeve member at which the outer sleeve is firmly fixed to the vehicle body.
In this mode (1) of the present invention, the first and second elastic protrusions may be spaced apart from the respective first and second stop portions in the axial direction, when the upper support is not subjected to an axial load. Alternatively, the first and second elastic protrusions are held in pressing contact with the first and second stop portions of the outer sleeve, in a static state of the upper support. In the latter case, the upper support permits an elimination of an impact noise generated by collision of the first and second elastic protrusions to the respective first and second stop portions upon application of the axial vibrational load to the upper support.
Various methods and structures may be employable in order to apply the radial compression force to the elastic body. For instance, the outer sleeve may be radially inwardly drawn onto the elastic body disposed radially inwardly of the outer sleeve, whereby the elastic body is compressed in the radial direction.
(2) An upper support according to the above mode (1), wherein the elastic body is forcedly pressed into the outer sleeve member, whereby the elastic body is compressed by the outer sleeve member in the radial direction. In this mode (2) of the present invention, a desired radial compression force is applied to the elastic body with ease and prompt.
According to one advantageous arrangement of this mode (2), the outer circumferential surface of the elastic body and the inner circumferential surface of the outer sleeve member are tapered so as to have respective diameters which decrease in a pressing direction in which the elastic body is pressed into the outer sleeve member. This arrangement facilitates not only manufacture but also assembly of the elastic body and the outer sleeve.
(3) An upper support according to the above mode (1) or (2), wherein the elastic body is subjected to an axial compression force applied to the axially opposite end faces thereof by the outer sleeve. In the present mode (3), a suitable compressive preload is applied to the elastic body in the axial direction as well as the radial direction, whereby the radial compression force is effectively applied to the elastic body by the outer sleeve member, resulting in an improved noise preventing or reducing effects of the upper support.
(4) An upper support according to any one of the above modes (1)-(3), the upper support further comprising: a first annular groove disposed between an abutting portion of the elastic body to the first stop portion and an abutting portion of the first elastic protrusion to the first stop portion, said first annular groove being open to the axially outward direction and continuously extending in the circumferential direction; and a second annular groove disposed between an abutting portion of the elastic body to the second stop portion and an abutting portion of the second elastic protrusion to the second stop portion, said second annular groove being open to the axially outward direction and continuously extending in the circumferential direction, the abutting portions of the elastic body and the first elastic protrusion with respect to the first stop portion being substantially independent of each other by the first groove disposed therebetween, and the abutting portions of the elastic body and the second elastic protrusion with respect to the second stop portion being substantially independent of each other by the second groove disposed therebetween.
The arrangement of this mode (4) is effective to avoid or reduce an adverse affect of the radial and axial compression forces applied to the elastic body on the first and second elastic protrusions, ensuring desired vibration absorbing or buffering effects of the first and second elastic protrusions. The provision of the first and second annular grooves permits the upper support to exhibit non-linear spring characteristics with ease. The provision of the first and second annular grooves is also effective to reduce an amount of transmission of axial loads applied between the inner member and the outer sleeve to the first and second elastic protrusions, thereby effectively preventing or reducing a relative displacement between abutting surfaces of the first and second elastic protrusions and the first and second stop portions, leading to effective prevention of the noises generated by impacts of the abutting surfaces of the first and second elastic protrusions to the first and second stop portions, respectively.